1. Field of the Invention
The present invention relates to an optical fiber switch employed with an optical fiber communication system or the like and, more particularly, to an improvement in a reflection mirror type optical fiber switch adapted to extend or retract a reflection mirror to or from a gap between a pair of opposing collimator lenses equipped with optical fibers so as to perform switching and coupling of optical fiber circuits.
2. Description of the Related Art
A 2xc3x972 optical fiber switch disclosed under a title xe2x80x9cEfficient electromechanical optical switchesxe2x80x9d (U.S. Pat. No. 5,742,712) belongs to the same category of the aforesaid reflection mirror type optical fiber switch. Referring to FIG. 10 and FIG. 11, a configuration of the foregoing conventional reflection mirror type 2xc3x972 optical fiber switch will be described. The switch employs collimator lenses 1 and 2, and a reflection mirror 3. For the rod lenses 1 and 2, SELFOC lens (SFL; a trade name), which has been developed and commercialized by Nippon Sheet Glass Co., Ltd. and is commercially available, may be used.
FIG. 10 illustrates the reflection mirror inserted between the collimator lenses of the switch, and FIG. 11 illustrates a state wherein the reflection mirror has been removed from an optical path. The switch is a reflection mirror type 2xc3x972 optical fiber switch constructed using the collimator lenses 1 and 2, and the reflection mirror 3. For the rod lenses 1 and 2, SELFOC lens (SFL) developed and commercialized by Nippon Sheet Glass Co., Ltd. and has been commercially available may be used. Optical characteristics, technical information, and typical applications of SELFOC lens have been released from Nippon Sheet Glass Co., Ltd. The foregoing type of switch has been extensively used in an optical wavelength demultiplexer/multiplexer (WDM), an optical splitter, various optical fiber switches, etc.
Referring to FIG. 10 and FIG. 11, the rod lenses 1 and 2 having a reference length of 0.25 pitch are disposed so that they oppose each other, with optical axes thereof aligned and a small gap provided between end faces thereof. The reflection mirror 3 is disposed so that it may be repeatedly moved into or out of the gap between the rod lenses 1 and 2 at right angles with respect to the optical axes. Reference characters F1, F2, F3, and F4 denote optical fibers installed to ferrules or sleeves (not shown) and assembled so that they are positioned symmetrically with the same amount of eccentricity from the optical axes of the rod lenses 1 and 2.
FIG. 10 shows the reflection mirror 3 that has been inserted between the rod lenses 1 and 2. In this case, light of a very small mode field that is emitted from the optical fiber F1 turns into a parallel beam having a mode field that has been expanded through the rod lens 1, and reaches the reflection mirror 3. The parallel beam is reflected by the reflection mirror 3 and turned into light having a reduced mode field through the rod lens 1 before being incident on the optical fiber F2.
Similarly, light of a very small mode field that is emitted from the optical fiber F3 turns into a parallel beam having a mode field that has been expanded through the rod lens 2, and reaches the reflection mirror 3. The parallel beam is reflected by the reflection mirror 3 and turned into light having a reduced mode field through the rod lens 2 before being incident on the optical fiber F4.
FIG. 11 illustrates the state wherein the reflection mirror 3 has been removed from the gap between the rod lenses 1 and 2. In this case, light of a very small mode field that is emitted from an optical fiber of the optical fiber assembly F1 turns into a parallel beam having a mode field that has been expanded through the rod lens 1, then enters and passes through the rod lens 2 to become light of a reduced mode field before entering an optical fiber of the optical fiber assembly F4. Similarly, light of a very small mode field that is emitted from an optical fiber of the optical fiber assembly F3 turns into a parallel beam having a mode field that has been expanded through the rod lens 2, then passes through the rod lens 1 to become light of a reduced mode field before entering an optical fiber of the optical fiber assembly F2. Hence, a circuit of the optical fiber F1 can be alternately coupled to a circuit of the optical fiber F2 or the optical fiber F4 by moving the reflection mirror 3 in or out. Similarly, a circuit of the optical fiber F3 can be alternately coupled to a circuit of the optical fiber F2 or the optical fiber F4 by moving the reflection mirror 3 in or out.
The conventional 2xc3x972 optical fiber switch set forth above has a simple construction, but poses the following problems:
(1) Insertion loss values present a repeatability problem and are susceptible to external influences, such as vibrations and shocks.
(2) Prone to malfunction from magnetic induction under the influences of external magnetic fields.
(3) Poses a structural problem in reducing a size of a switch package to a particular size, namely, a height of 8.5 mm or less to be applicable to a xc2xd inch printed circuit board.
The problem with the insertion loss values is caused by inconsistent stop positions of the reflection mirror 3. This problem will be described in detail with reference to FIG. 9.
When an angle error "sgr"xcex8 with respect to a plane at right angles to an optical axis ZZ of the reflection mirror 3 occurs, a reflection angle of a parallel beam that has been transmitted through the rod lens 1 from the optical fiber assembly F1 and reflected by the reflection mirror 3 will be smaller by xe2x88x922"sgr"xcex8. As a result, the parallel beam is emitted to a point decentered inward from an optical axis of the optical fiber assembly F2, leading to the occurrence of an insertion loss attributable to a dislocated axial center. Similarly, a reflection angle of a parallel beam that has been transmitted through the rod lens 2 from the optical fiber assembly F3 and reflected by the reflection mirror 3 will be larger by +2"sgr"xcex8. The parallel beam is emitted at a point Q decentered outward from an optical axis of the optical fiber F2, resulting in an increased insertion loss.
According to calculated values, if a rod lens having an outside diameter of 2 mm and a pitch of 0.25 are used, two single-mode optical fibers are decentered 0.0065 mm from an optical axis of the rod lens, and a wavelength of 1310 nm is used, then an optical insertion loss will be approximately 1 dB (≈xe2x88x9220%) when an optical squareness error is as follows: "sgr"xcex8=0.024xc2x0. Incidentally, the squareness error is extremely small (tan 0.024xc2x0≈0.00042); therefore, if variations in a mechanical position of repeated insertion of the reflection mirror 3 exceed 0.024xc2x0, then variations in optical insertion loss will be approximately 1 dB (≈xe2x88x9220%). If the reflection mirror moves due to external forces, such as vibrations or shocks, when the reflection mirror is inserted between the rod lenses, then similar optical insertion loss will incur variations of approximately 1 dB (≈xe2x88x9220%).
In the optical switch disclosed in U.S. Pat. No. 5,742,712, to drive a reflection mirror, the reflection mirror is installed on a distal end of a swing arm attached to a movable piece of a seesaw electric relay. By switching a polarity of current supplied to the seesaw electric relay, a reflection mirror surface at the distal end of the swing arm provided with the reflection mirror is moved into or out of the gap between rod lens surfaces so as to perform switching. This structure in which the reflection mirror is installed on the distal end of the swing arm attached to the movable piece retained by a very small magnetic force of the seesaw electric relay has limitation in reducing size and weight. Furthermore, it is presumed that assembly and adjustment is extremely difficult.
Regarding the shortcoming described in (1) above, it is presumed that the repeatability of accurate positioning of the reflection mirror is extremely deteriorated, and that the optical switch is extremely susceptible to external forces, including vibrations and shocks.
Regarding the shortcoming described in (2) above, in the case of a reflection mirror type optical fiber switch in a patent example, a small electromagnetic solenoid and an electric relay using a permanent magnet are employed as a drive source of the reflection mirror. It has been reported that there is a possibility of a movable piece being moved with resultant malfunction if subjected to an intense external magnetic field.
Regarding the shortcoming described in (3) above, reducing a volume is limited in obtaining a required driving force by the electromagnetic solenoid and the electric relay using a permanent magnet. This means that it is difficult to house the device in a package having a height of 8.5 mm or less from a viewpoint of design. Incidentally, it is mentioned in the foregoing patent example that the height of the package of the reflection mirror type optical fiber switch is 20 mm.
Accordingly, an object of the present invention is to provide a reflection mirror type optical fiber switch that has solved the problems with the conventional reflection mirror type optical fiber switch described above. To be more specific, the reflection mirror type optical fiber switch in accordance with the present invention is intended to:
(1) exhibit smaller insertion loss values, provide stable repeatability, and resist external forces, such as vibrations or shocks;
(2) minimize chances of malfunction caused by external magnetic induction; and
(3) be able to be mounted on a xc2xd inch printed circuit board, a height of a package being 8.5 mm or less.
In other words, an object of the present invention is to provide a reflection mirror type optical fiber switch that satisfies the three requirements listed above.
To this end, according to one aspect of the present invention, there is provided a reflection mirror type 2xc3x972 optical fiber switch, comprising a first collimator lens assembly C1 having a pair of optical fibers F1 and F2 disposed symmetrically with respect to an optical axis of a lens, a second collimator lens assembly C2 having a pair of optical fibers F3 and F4 disposed symmetrically with respect to an optical axis of a lens, an aligning block B in which the first and second collimator lens assemblies are opposed each other with their optical axes aligned, and supported so that the optical fiber F1 and the optical fiber F4 are optically coupled and the optical fiber F2 and the optical fiber F3 are optically coupled, a reflection mirror assembly formed by a reflection mirror shaft rotatably installed in a shaft hole provided in parallel to an optical axis of the lens in the aligning block, a reflection mirror provided on the reflection mirror shaft so that the reflection mirror can move between a first position where the reflection mirror reflects light from the optical fibers to focal surfaces of the lenses at right angles to the optical axes of the lenses and a second position where the reflection mirror causes the light from the optical fibers to directly enter the focal surfaces of the lenses, and defining means for defining a position of the reflection mirror at the first position by using the aligning block as a reference, and driving means for driving the reflection mirror.
Each of the first and second collimator lens assemblies is formed of a pair of optical fibers, a ferrule supporting the optical fibers, and a rod lens of about 0.25 pitch which is coupled to the optical fibers and an end of the ferrule.
The driving means employs a micro motor wherein a portion to be engaged with the reflection mirror assembly is provided in an end of a rotating shaft.
The reflection mirror uses a metal, such as stainless steel, as a material thereof, and both surfaces of the metal are provided with Tixe2x80x94N coating of a hardness of MHv 1800 or more and coated with a film having high reflectivity, such as gold (Au) or platinum (Pt), by sputtering or chemical plating.
A permanent magnet in the vicinity of or in contact with the rotating shaft of the reflection mirror is buried in the aligning block to provide a self-holding mechanism at an end of a rotational angle of the reflection mirror.
To this end, according to one aspect of the present invention, there is provided a reflection mirror type 1xc3x972 optical fiber switch, comprising a first collimator lens assembly C1 in which a pair of optical fibers F1 and F2 is disposed in parallel symmetrically with respect to an optical axis of a lens, with a predetermined gap d being maintained therebetween, a second collimator lens assembly C2 in which a single optical fiber F4 is disposed in parallel to an optical axis of a lens, with a gap d/2 from the optical axis being maintained, an aligning block B in which the first and second collimator lens assemblies are opposed to each other with their optical axes aligned, and supported so that the optical fiber F1 and the optical fiber F4 are optically coupled, a reflection mirror assembly formed by a reflection mirror shaft rotatably installed in a shaft hole provided in parallel to an optical axis of the lens in the aligning block, a reflection mirror provided on the reflection mirror shaft so that the reflection mirror can move between a first position where the reflection mirror reflects light from the optical fibers to focal surfaces of the lenses at right angles to the optical axes of the lenses, and a second position where the reflection mirror causes the light from the optical fibers to directly enter the focal surfaces of the lenses, and defining means for defining a position of the reflection mirror at the first position by using the aligning block as a reference, and driving means for driving the reflection mirror.
To this end, according to one aspect of the present invention, there is a reflection mirror type 1xc3x971 optical fiber switch, comprising in a reflection mirror type optical fiber switch having a collimator lens assembly formed by a pair of the optical fibers disposed symmetrically with respect to an optical axis of a lens, and a reflection mirror set at a focal position of the lens and moved between a first position for making connection from one optical fiber to another optical fiber, and a second position where the reflection mirror is retracted from the focal position, an aligning block supporting the collimator lens assembly and the reflection mirror, a reflection mirror assembly formed by a reflection mirror shaft rotatably installed in a shaft hole provided in the block in parallel to the optical axis of the lens, a reflection mirror provided on the reflection mirror shaft and extended to or retracted from image forming surfaces of the optical fibers at right angles to the optical axes of the lenses, and defining means for defining position of the reflection mirror at the first position based on the aligning block, and driving means for driving the reflection mirror.
The defining means is formed by a plane formed at right angles to an optical axis of the lens mounted on the aligning block, and a reflection mirror or a flange that rotates in slidable contact with the plane.